The physical basis of heredity remained obscure. Although Mendelian particles must exist, where are they housed within cells? Following the rediscovery of Mendel’s work in 1900, questions arose as to where such entities (genes) might reside and exactly how Mendelian laws might be physically underpinned. The answers soon would be forthcoming.
Mendelian particles; chromosomes
The physical basis of heredity remained obscure. Although Mendelian particles must exist (see Chapter 3), where are they housed within cells? Following the rediscovery of Mendel’s work in 1900 (see Chapter 11), questions arose as to where such entities (genes) might reside and exactly how Mendelian laws might be physically underpinned. The answers soon would be forthcoming.
In 1902, Walter Sutton and Theodor Boveri independently discerned the link between Mendel’s abstract hereditary factors and tangible structures known as chromosomes that cytologists had discovered in the late 1800s. Sutton’s work – based on his Master’s thesis – entailed cytological observations on the large chromosomes of the landlubber grasshopper (Brachystola magna). Under a microscope, Sutton watched as the pairs of chromosomes segregated and sorted independently during gamete formation, in a nicely parallel fashion to the deduced behavior of Mendelian particles. Sutton (1902) was crystal clear in his paper’s understated final sentence (p. 39): “I may finally call attention to the probability that the association of paternal and maternal chromosomes in pairs and their subsequent separation during the reducing division … may constitute the physical basis of the Mendelian law of heredity.” This cytological work on autosomes (nuclear chromosomes other than the sex chromosomes) was soon confirmed and extended in the laboratory of Thomas Hunt Morgan (see Chapter 14), and it later led to what E. B. Wilson (1925) termed the “Sutton-Boveri” chromosomal theory of inheritance.
This breakthrough merits a high score because it provided the needed link between deduced Mendelian particles and the physical structures (chromosomes) on which they reside. The chromosomal theory of inheritance has fully withstood the tests of time. Today, we know that chromosomes are the physical structures that house genes in essentially all organisms, and that their cellular behaviors during meiosis and syngamy basically account for Mendel’s laws of inheritance in sexually reproducing taxa.
In an interesting footnote to this story, the term “genome” (see Chapter 66) apparently traces to a merger in 1920 of “gene” with “chromosome” by the German botanist Hans Winkler (Lederberg and McCray, 2001).
1. Sutton WS. On the morphology of the chromosome group in Brachystola magna. Biol Bull. 1902;4:24–39.
2. Sutton WS. The chromosomes of heredity. Biol Bull. 1903;4:231–251.
3. Wilson EB. The Cell in Development and Heredity 3rd edition New York, NY: Macmillan; 1925.
4. Lederberg J, McCray AT. ’Ome sweet ’omics: a genealogical treasury of words. The Scientist. 2001;15:8.
5. Crow EW, Crow JF. Walter Sutton and the chromosome theory of heredity. Genetics. 2002;160:1–4.